Ceramic materials have important industrial applications, and generally comprise natural porosity. Often, the natural porosity is determined by the composition and the grain structure of the raw materials. The ceramic materials require good thermal stability, thermal and electrical insulation, good refractory properties and reduced weight. The natural porosity is, in most instances, insufficient to confer such properties to the ceramic materials.
Ceramic materials with higher porosity levels than those of natural porosity can be obtained by various methods known in the art. Most often, such higher levels of porosity can be achieved by using porogens or pore-forming materials such as graphite, polymer beads or fibers which can be removed in subsequent heating steps without leaving any residues.
Even though higher porosity levels are desirable for many applications, introducing higher porosity levels also decrease the mechanical strength of the ceramic materials. This problem is partially addressed by prior art methods, for example, by controlling the homogeneity of pore size distribution. In these instances, a homogenizing agent is added to the ceramic precursor mixture to control the pore size distribution.
Additionally, most of the known methods lack the ability to prepare ceramic materials with pre-determined porosity and pre-determined pore connectivity. Ceramic materials with three-dimensional network of interconnected pores can have several important technological applications. Furthermore, it is impossible to use any of the known methods to prepare porous ceramic materials with large pore sizes, especially in the range of 3 mm to 11 mm. Based on the literature, the macroporous ceramic materials can only be obtained using high tech ceramics such as yttrium, zirconium and alumina based ceramic forming materials. Even with such high tech ceramics, it is not possible to obtain microporous ceramics with pore sizes of larger than 1-2 mm.
U.S. Pat. No. 6,547,967 to Adler et al. discloses a method of forming a ceramic network. According to Adler, a fiber network is impregnated with a ceramic suspension, the resultant intermediate is dried, fiber network is removed, and the resultant structure is sintered to obtain the ceramic struts. Upon the removal of fiber network, a network of cavities, akin to a capillary network (as determined by the fiber network) is created based on the fiber network. The ceramic struts are interconnected via cavities. Adler's method does not create a network of cavities and pores, and as such this method does not create a network of interconnected pores. In this method, the cavities are not interconnected via a network of three-dimensional pores. Adler's method produces cavities of size about 150 μm and 350 μm (Example 1 and 2). High tech ceramics such as SiC and Al2O3 have been used in this method.
As such, it is advantageous to discover a cost-effective, efficient and viable method to prepare macroporous ceramic materials.